Hydrogen gas is prevalent in many commercial and industrial settings. There is currently a need for a small, rugged, inexpensive hydrogen sensor for applications where hydrogen is used, produced, or may potentially harm equipment or processes. Hydrogen sensor applications include lead-acid battery storage and charging stations, furnaces, electric power plants, petroleum processing plants, submarines, hydrogen-fueled vehicles, and radioactive waste tanks.
There are prior art hydrogen sensors, including thin-film sensors fabricated from optical fibers. Such prior art discloses thin-film, hydrogen sensing systems such as the ones represented by the sensing element 100 illustrated in FIG. 1A and the sensing element 110 illustrated in FIG. 1C. Referring to FIG. 1A and the corresponding cross section in FIG. 1B, we see that the fiber sensing element 100 is comprised of a silica core 101 with the outer cladding removed, a first layer 102 of transparent silicone resin circumferentially deposited about the core 101, and a second layer 103 of silicone resin dispersed with a palladium-supported tungsten oxide powder.
Referring to FIG. 1C and the corresponding cross section in FIG. 1D, we see that the second sensing element 110 is comprised of a silica core 111 of an optical fiber with the outer cladding removed and a layer 112 formed using a sol-gel technique. More specifically, the layer 112 includes tungsten and palladium impregnated into the silica core by dip-coating the optical fiber in an aqueous solution of sodium tungstate. The sensing element 110 is subsequently calcined at 500 degrees Celsius for three hours.
The presence of hydrogen is determined with the sensing elements 100, 110 by analyzing the reflectance spectra at the upper end of the visible spectrum or the transmission spectra at one or more wavelengths between 530 and 800 nanometers.
In comparison to the present invention, each of these prior art sensing elements is relatively insensitive to hydrogen gas because the reactive component, the tungsten and palladium mixture, is confined to the relatively thin and discrete layers 103, 112 at the outermost portion of the optical fiber. Furthermore, the prior art sensing elements 100, 110 exhibit long recover times and limited sensitivity to relatively high concentrations of hydrogen.